Voltage points and negative to ground.

电压分，负向地面。

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DC voltage is always positive (or always negative), but it may increase and decrease.

交流电压总是正极(或总是负极)，它一样会增殖或减殖。

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DC voltage is always positive (or always negative), but it may increase and decrease.

交流电压总是正极(或总是负极)，它一样会增殖或减殖。

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